Abstract The Children?s Health and Air Pollution Study (CHAPS), one of the NIEHS/EPA co-sponsored Children?s Environmental Health Centers, has focused on the effects of air pollution on children growing up in the San Joaquin Valley of California, one of the most polluted areas in the country. CHAPS involves the recruitment and follow-up of two age-specific cohorts of children, an infant cohort recruited while in utero and a child cohort recruited at ages 6-8. The primary research goal for both cohorts is to investigate the effects of exposure to ambient air pollution, particularly polycyclic aromatic hydrocarbons (PAHs) and other traffic-related pollutants, on immune and metabolic dysregulation. We have recruited over 200 children in each of the two cohorts and are in the process of following them over a 2-year period. We have collected the following biomarker data: anthropometry; blood pressure (BP); spirometry in the child cohort; assays in blood samples for immune regulation, metabolic function, and systemic inflammation; and a urinary assay for oxidative stress. To date, our research team has a) confirmed a novel epigenetic mechanism by which ambient PAHs and other pollutants contribute to allergic disease in children through hypermethylation of the forkhead box P3 gene (FOXP3), b) confirmed that exposure to ambient PAHs is associated with reduced lung function in children, and c) shown that exposure to traffic-related air pollutants, including ambient PAHs, is associated with BP, hemoglobin A1c (HbA1c), BMI-for-age, and urinary 8-isoprostane. Whether our findings in young children will predict future allergic disease and metabolic syndrome as the children age is an important and currently unanswered question. To address this question we propose in our application for Environmental Epidemiology Cohort (EEC) funding the following specific aims: 1) to retain and continue to follow both CHAPS infant and child cohorts over the next 5 years; 2) to maintain and strengthen data management infrastructure; 3) to maintain and enrich the CHAPS repository of biospecimens; 4) to conduct validation, pilot, and feasibility studies using existing data and samples; and 5) to encourage data sharing. The well-characterized CHAPS cohorts provide the opportunity to study the health effects of traffic-related air pollution from birth through adolescence in a low-income, predominantly Latinx community. The proposed EEC will provide evidence in support of policies to protect the health of such vulnerable communities.